printing apparatus and a method for controlling the transport of sheets through a printing apparatus

ABSTRACT

The invention relates to a printing apparatus and a method for controlling the transport of sheets through a printing apparatus, in particular a digital printing apparatus. The printing apparatus has at least one print module and a transport arrangement defining a direction of transport, arranged for transporting sheets past said at least one print module for printing thereon. In the method for controlling the transport of sheets through the printing apparatus, a print queue is set by assigning images to respective sheets, prior to feeding the respective sheets into the transport arrangement. The sheets are then fed into the transport arrangement, an it is detecting whether a double sheet feeding has occurred. Superposed double sheets are deflected to a double sheet box, which is arranged upstream of the at least one print module, and at least those sheets following the superposed double sheet in the transport arrangement, for which an image has already been assigned and which are not in a duplex path, are guided to a waste box, which is arranged downstream of the at least one print module. Finally, the print queue is automatically reset and printing is continued without stopping the printing apparatus.

FIELD OF THE INVENTION

The present invention relates to a printing apparatus and a method forcontrolling the transport of sheets through a printing apparatus, inparticular a digital printing apparatus. In particular, the invention isdirected towards handling the occurrence of a double sheet event in atransport arrangement of the printing apparatus.

BACKGROUND OF THE INVENTION

In the field of digital printing it is known to have a printingapparatus having at least one print module and a transport arrangementdefining a direction of transport and being arranged for transportingsheets past said at least one printing module for printing thereon.Sheets to be printed are typically fed to the transport arrangement froma paper feed device, which typically feeds sheets one by one into thetransport arrangement. During the feeding of the sheets, it may occurthat two (or more) sheets are fed into the transport arrangement in asuperimposed manner, which occurrence is designated herein as a doublesheet event. Such a double sheet event, if undetected, typically leadsto a paper jam during the transport of the superimposed sheets throughthe printing apparatus. If such a paper jam occurs, all the sheetscurrently in the transport arrangement have to be manually removed andthe printing apparatus has to be manually reset to allow a restartthereof. Even though double sheet events only occur sporadically, theymay lead to considerable downtime of a printing apparatus during anextended period of time.

In order to avoid a paper jam due to a double sheet event and the needto manually remove the sheets from the transport arrangement, differentapproaches have been taken in the past.

In one approach, which was used in the NexPress 2001 “Classic”, a doublesheet waste tray was used between a paper feed device and a print moduleof the NexPress 2001. Upon detection of a double sheet event, thesuperimposed sheets were diverted towards the waste tray in order toavoid a paper jam. Subsequently, all sheets in the transport path of theprinting apparatus were purged into the proofing tray of the printingapparatus. After the purging, the printing apparatus was automaticallystopped and the operator was notified. The operator then had to manuallyclear the proofing tray and had to manually reset the printing apparatusfor a restart thereof. Even though this system may reduce down time ofthe printing apparatus due to the fact that sheets in the transport pathdid not have to be removed manually, its still requires substantialinput and time of an operator. Furthermore, inasmuch as all sheets inthe paper path are purged to the proofing tray in the above system, alarge number of waste paper is generated.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention, to overcome one ormore of the disadvantages of the prior art.

In accordance with the present invention, a method for controlling thetransport of sheets through a printing apparatus as set forth in claim 1and a printing apparatus as set forth in claim 8 are provided. Furtherembodiments of the invention are claimed in the dependent claims.

In method for controlling the transport of sheets through a printingapparatus having at least one print module and a transport arrangementdefining a direction of transport, which is arranged for transportingsheets past the at least one print module for printing thereon, a printqueue is set by assigning images to respective sheets prior to feedingthe respective sheets into the transport arrangement. After sheets arefed into the transport arrangement, it is detected whether a doublesheet feeding has occurred. Upon detecting a double sheet feeding, thedouble sheets are deflected to a double sheet box which is arrangedupstream of the at least one print module. Furthermore, at least thosesheets following the double sheets in the transport arrangement, forwhich an image has already been assigned and which are not in a duplexpath, are guided to a waste box which is arranged downstream of the atleast one print module. Finally, the print queue is automatically resettaking into account those sheets deflected towards the double sheet boxand the waste box, and printing is continued without stopping the printapparatus. The above method thus provides an automated process forhandling double sheet events in an efficient manner without the need foroperator intervention.

In accordance with an aspect of the invention, the printing apparatushas at least one print module, at least one sheet supply including afeeder and a transport arrangement defining a transport path having adirection of transport, which transport path is arranged fortransporting sheets from said sheet supply past the at least one printmodule to a sheet output. The printing apparatus also has a double sheetsensor arranged to sense a double sheet event, i.e. occurrence of twosuperimposed sheets on said transport arrangement, which double sheetsensor is arranged downstream of said paper supply and upstream of saidat least one print module in the direction of transport. A double sheetbox is arranged downstream of the double sheet sensor and upstream ofthe at least one print module in the direction of transport. A firstdeflector is provided, which is operable to selectively deflect sheetson said transport arrangement towards the double sheet box. The printingapparatus has a waste box arranged downstream of said at least one printmodule and a second deflector operable to selectively deflect sheets onsaid transport arrangement towards said waste box. Such printingapparatus allows in an efficient manner handling of a double sheetevent. By separating a double sheet box from a waste box it is possibleto guide sheets correctly fed into the transport arrangement towards thewaste box past the at least one print module which may facilitatestabilizing the print process.

The foregoing and other objects, features and advantages of theembodiments will be apparent from the following more detaileddescription of exemplary embodiments of the method and apparatus, asillustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an electro photographic printingapparatus;

FIG. 2 is a schematic timeline of certain events taking place during theelectro photographic printing process;

FIG. 3 is a simplified schematic side view of an electro photographicprinting apparatus showing a normal operation of the printing apparatus;

FIG. 4 is a simplified schematic side view of an electro photographicprinting apparatus showing a first application of the method forcontrolling the transport of sheets through the printing apparatus;

FIG. 5 is a simplified schematic side view of an electro photographicprinting apparatus showing an alternative application of the method forcontrolling the transport of sheets through the printing apparatus.

DETAILED DESCRIPTION OF THE INVENTION

The following description uses relative terms such as left right aboveand below, which relative terms refer to the drawings and should not beconstrued to limit the application.

FIG. 1 shows a schematic side view of an electro-photographic printingapparatus 1. The printing apparatus 1 has a housing 3 for mountingdifferent elements therein or thereon, as will be described in moredetail herein below. Within the housing 3, a transport arrangement 6defining a transport path 7 is provided. The following are arrangedwithin the housing 3 along the transport path 7: a sheet supply 9, adouble sheet sensor arrangement 11, a double sheet box 13, asheet-aligner 15, a print unit 17, a fuser 19 and an inverter 21.

External to the housing a proofing tray 23, a sheet output 25 and awaste box 27 are provided. Even though these elements are shown outsideof the housing 3, they may also be integrated within the housing 3.

The transport arrangement 6 may be of any suitable type for transportinga sheet along the transport path through the printing apparatus 1 and toa sheet receptacle, such as the double sheet box 13, the proofing tray23, the sheet output 25 or the waste box 27. The transport arrangement 6as a whole may be formed by a plurality of individual transport devices,which are driven by respective drives and controlled by a controller,for synchronization of a sheet transport throughout the printingapparatus 1. Sheets, which are fed from the sheet supply 9 into thetransport path 7 are moved along a direction of transport as indicatedby arrow A throughout the printing apparatus 1.

The sheet supply 9 has a storage compartment 30 for storing a stack ofsheets 32 and a feeder (not shown) for feeding sheets 32 into thetransport path as indicated by the dashed line B. The sheet supply 9 canbe of any suitable design for feeding individual sheets 32 into thetransport path 7. Even though, FIG. 1 only shows a single sheet supply9, several sheet supplies, which may for example hold different types ofsheets may be provided. These sheet supplies may be arranged in a mannerthat the sheets are in substance fed into the transport arrangement 6 atthe same position.

The double sheet sensor arrangement 11 is arranged downstream along thetransport path 7 with respect to the sheet supply 9. The double sheetsensor arrangement 11 may be of any suitable for detecting a doublesheet event, i.e. the occurrence of two superposed sheets 32 in thetransport path 7. The double sheet sensor arrangement 11 is connected toa controller (not shown) to initiate appropriate action in the event ofa double sheet event, as will be described in more detail herein below.

The double sheet box 13 is arranged downstream of the double sheetsensor arrangement 11 along the transport path 7. The double sheet box13 has a compartment 34 for receiving a plurality of sheets 32, and adeflector 35, for deflecting sheets from said transport path 7 towardsthe compartment 34. As shown in FIG. 1, the deflector 35 is movablebetween a non-deflecting position shown by the solid line and adeflecting position shown by a dashed line in FIG. 1. As will bedescribed in more detail herein below, the deflector 35 is typically inthe non-deflecting position, and only upon occurrence of a double sheetevent it is moved towards the deflecting position in order to guidesuperposed sheets in the transport path towards the compartment 34. Thedouble sheet box may have means for monitoring the fill level thereof,as a full double sheet box may lead to a paper jam scenario. On way ofmonitoring is counting the double sheet events and giving out a noticeto the operator to clear the double sheet box after a certain amount ofdouble sheet events, to thereby avoid overfilling the double sheet box.Emptying of the double sheet box may also be monitored, for example by asafety switch indicating opening of the double sheet box, which is thentaken as an indicator, that it is emptied. Also a sensor directlysensing the fill level of the double sheet box may be provided.

The sheet aligner 15 is arranged downstream of the double sheet boxalong the transport path 7. The sheet aligner 15 may be of any suitabletype for aligning sheets 32 in the transport path for example withrespect to skew, with respect to a cross track position, i.e. at rightangle to the direction of transport A, and with respect to an in-trackposition, i.e. in the direction of transport A. The sheet aligner 15 mayhave a pre-alignment section 37 and a final alignment section 38, as isknown in the art.

The print unit 17 is arranged downstream of the sheet aligner 15 and mayhave one or more electro-photographic print modules 40. The printingapparatus 1 as shown in FIG. 1 has five electro-photographic printmodules 40 for the application of toner onto a sheet 32, in a knownmanner. Depending on the application, a lower or higher number ofprinting modules 40 may be provided.

Downstream of the printing unit 17 a fuser 19 is provided. The fuser 19may be of any suitable type for fusing toner applied by the printmodules 40 to a sheet 32. The fuser 19 may be of a contact type usingfor example fusing rollers and/or a fuser belt, or of a non-contact typeusing for example UV-radiation or microwaves for fusing a toner to asheet. The type of fuser 19 is at least partially dependent on the tonerused in the print module 40.

Downstream of the fuser 19, a guide 42 is provided for selectivelyguiding a sheet 32 in the transport path 7 towards the proofing tray 23,the sheet output 25 or downwards towards the waste box 27 or inverter21. The guide 42 may be of any suitable design as will be apparent to askilled person for guiding a sheet along one of the selected paths.

A further guide 44 is provided downstream of the guide 42 along thetransport path 7, for selectively guiding a sheet 32 towards the wastebox 27 or further along the transport path 7 to inverter 21 for duplexprinting of the sheet. The guide 44 may again be of any suitable typefor guiding a sheet in the desired direction.

Inverter 21 is arranged downstream of the guide 44 along the transportpath 7 and upstream of the sheet supply 9. The sheet inverter 21 is ofany suitable type for inverting a sheet in the transport path, to allowduplex printing of a sheet 32. Inverter 21 is preferably of a type, inwhich the sheet is inverted in such a manner, that the leading edge ofthe sheet is not changed during the inversion process.

The section of the transport path 7 extending between sheet supply 9 tothe guide 42 may be called a simplex path, while the section extendingbetween guide 42 and sheet supply 9 may be called a duplex path.

The proofing tray 23 may be any suitable tray for receiving sheets 32thereon for proofing purposes, as known in the art. The sheet output 25may again be of any suitable design for receiving printed sheets 32. Asshown in FIG. 1, the sheet output 25 has a tray 46, which may be movedup and down, as indicated by double-headed arrow C, depending on thenumber of sheets stacked thereon.

Similarly, the waste box 27 may be of any suitable design for receivinga plurality of sheets, and may have the same general structure as thesheet output 25, including a tray 48 which is movable up and down asindicated by the double-headed arrow D in FIG. 1. Sheet output 25 istypically much larger than waste box 27 as it is expected to receive amuch higher number of sheets.

In the following, normal operation for simplex printing of sheets in theprinting apparatus 1 will be described with reference to FIGS. 1 to 3.FIG. 2 shows a schematic time line of different events taking placeduring the printing process, while FIG. 3 shows a simplified schematicof the printing apparatus used for explaining printing operation.

In FIG. 3, the same reference signs as used in FIG. 1 will be used forequivalent or similar elements. The simplified view of FIG. 3 shows atransport path 7, a sheet supply 9, a double sheet sensor arrangement11, a double sheet box 13, a print module 40, a waste box 27 and aninverter 21, which are arranged along the transport path 7 in the abovereferenced order.

FIG. 3 also shows so-called frames 50, 50′, corresponding to desiredsheet positions along the transport path, to which virtual images in aprint queue are assigned, as will be explained in more detail hereinbelow. The frames 50 represent frames which are synchronized with thevirtual images, while frames 50′ show unsynchronized frames. As will beobvious to the skilled person, the frames 50, 50′ are not stationary butmove along the transport path in accordance with the speed of thetransport arrangement and FIG. 3 only shows the respective framepositions at an exemplary point in time. Where sheets 32 are present inthe position of a frame 50, this is shown by hatching.

At 52 a print queue for the printing process, which corresponds toelectrical signals, is represented in a schematic manner. Reference sign54 represents a virtual image in the print queue, which is to be printedonto a sheet 32 in print module 40.

As indicated in FIG. 2, at a time T_(assign), an image will be assignedto a frame 50′ in accordance with a print job. At a time T_(sync), thisframe is synchronized with the assigned image, taking into account thespeed of the transport arrangement 6, and the print module 40, toachieve a synchronized frame 50. At a time T_(feed), a sheet 32 is fedinto the position of a frame 50 (as indicated by showing the frame 50hatched in FIG. 3). After the sheet has been fed into the frameposition, at a time T_(dsd) it is detected, whether more than one sheetis present in a frame position (i.e. a double sheet event has occurred),which is not the case during normal operation. If no double sheet eventhas occurred, the sheet 32 is then further transported towards the printmodule 40, where an image is printed onto sheet 32 in accordance withthe previous assignment.

Even though not shown in FIG. 3, proper alignment of a sheet 32 with itssynchronized frame position 50 may be achieved in an aligner 15 as shownin FIG. 1. Furthermore, FIG. 3 only shows a single print module 40, butthe skilled person will realize that further print modules may beprovided, each for example printing a single color image onto the sheet32, in order to generate a multi-color image. After printing an imageonto the sheet, the image is fused thereto and the sheet can be guidedtowards a sheet output, which is not shown in FIG. 3. The aboverepresents normal operation of a simplex printing operation for a sheet32.

In a duplex printing operation, the sheets, after fusing the imagethereto would not be guided to a sheet output, but into a duplex sectionof the transport path 7, as explained with respect to FIG. 1. The sheetwould then be inverted in the inverter 21 and images would then beassigned to the thus inverted sheets in accordance with theircorresponding frame positions.

FIG. 4 shows a simplified schematic side view of an electro-photographicprinting apparatus corresponding to FIG. 3, showing the occurrence of adouble sheet event during a simplex printing operation. In accordancewith FIG. 4, a first application of a method for controlling thetransport of sheets through the printing apparatus upon occurrence of adouble sheet event will be described. In FIG. 4 the same reference signswill be used as used in FIG. 3.

Operation is identical to the operation previously described up untilthe point, that a double sheet event is detected by the double sheetsensor arrangement 11. If such a double sheet event is detected, all thesheets 32, which were fed into the transport path 7 upstream of thesuperposed sheets 32 are handled in the normal manner, i.e. an image inaccordance with the assigned virtual image in the print queue is printedthereon in print module 40. Subsequently these images are fused to therespective sheet and the sheet is then guided to the sheet output.

The virtual image 54 in print queue 52 which was assigned to the frame50, in which the double sheet event has occurred is deleted, and all ofthe virtual images 54 in the print queue 52 already assigned to frames50, 50′ downstream of the frame 50, in which the double sheet event hasoccurred are also deleted from the print queue. The superposed sheets inthe frame 50, in which the double sheet event has occurred, aredeflected towards the double sheet box 13 by activating the deflector 35to move into the deflecting position, as shown by the dashed line. Anysheets 32, which have already been fed into a transport path 7downstream of the frame 50, in which the double sheet event hasoccurred, are guided through print module 40 into waste box 27. Inasmuchas the virtual images have been deleted from the print queue 52, noimages are printed onto these sheets 32. Feeding to those framepositions 50, 50′, to which virtual images 54 had previously beenassigned in the print queue 52, but which are now deleted is stopped.

The print queue 52 is then automatically reset by re-assigning thevirtual image previously assigned to the frame 50, in which the doublesheet event had occurred to a new frame 50′, which frame 50′ is arrangeddownstream of the frames 50, 50′, to which a virtual image had beenassigned, but which were deleted from the print queue 52. Subsequently,these frames 50′ are synchronized and sheets are feed into the positionof the thus synchronized frames 50, in order to resume normal printingoperation. It is possible to feed a sheet 32 to a position of a frame(or several frames) which is (are) arranged upstream of the first frame,to which an image has been reassigned. These sheets are guided throughthe print module without printing thereon and may subsequently be guidedto the waste box 27. These sheets may act as so-called leader sheets forstabilizing the printing process, as known in the art.

The method described above, thus allows continuous operation of aprinting apparatus despite the occurrence of a double sheet event withinthe transport path.

FIG. 5 shows another simplified schematic side view of anelectro-photographic printing apparatus corresponding to FIG. 3, showingthe occurrence of a double sheet event during a duplex printingoperation. In accordance with FIG. 5, a second exemplary application ofa method for controlling the transport of sheets through the printingapparatus upon occurrence of a double sheet event will be described. InFIG. 5 the same reference signs will be used as used in FIG. 3. Inasmuchas FIG. 5 shows a duplex mode of operation, several sheets are shown,which are in the duplex path (i.e. an image has been printed on one sideand they are inverted for printing on the reverse side thereof), thesesheets are indicated by solid frames 58 in FIG. 5.

Operation is identical to the operation previously described up untilthe point, that a double sheet event is detected by the double sheetsensor arrangement 11. If such a double sheet event is detected, all thesheets 32, which were fed into the transport path 7 upstream of thesuperposed sheets 32 are handled in the normal manner, i.e. an image inaccordance with the assigned virtual image in the print queue is printedthereon in print module 40. Subsequently these images are fused to therespective sheet and the sheet is then guided into the duplex path.

The virtual image 54 in print queue 52 which was assigned to the frame50, in which the double sheet event has occurred is deleted. Also thosevirtual images 54 in the print queue 52, which have been assigned toframes 50 downstream of the frame 50, in which the double sheet eventhas occurred, and which frames do not belong to sheets in the duplexpath are also deleted from the print queue 52. Those virtual images 54assigned to frames 58, i.e. to frames belonging to sheets in the duplexpath, remain in the print queue.

The superposed sheets in the frame 50, in which the double sheet eventhas occurred, are deflected towards the double sheet box 13 byactivating the deflector 35 to move into the deflecting position, asshown by the dashed line. Any sheets 32, which have already been fedinto the transport path 7 downstream of the frame 50, in which thedouble sheet event has occurred, and which are not in a duplex run areguided through print module 40 into waste box 27. Inasmuch as thevirtual images have been deleted from the print queue 52, no images areprinted onto these sheets 32. Feeding to those frame positions 50, 50′,to which virtual images 54 had previously been assigned in the printqueue 52, but which are now deleted is stopped. It is, however, possibleto feed a sheet 32 to a position of a frame (or several frames) which is(are) arranged upstream of the first frame 58, i.e. a frame belonging toa sheet which is in a duplex run. This (these) sheet(s) is (are) guidedthrough the print module without printing thereon and may subsequentlybe guided to the waste box 27. This (these) sheets may act as so-calledleader sheets for stabilizing the printing process, as known in the art.

Those sheets in frames 58 are guided through the print modules andprinting on these sheets is performed in accordance with the virtualimages 54 in the print queue 52, as these images were not deletedtherefrom. Subsequently these images are fused to the sheets and thesheets are guided towards the sheet output 25.

The print queue 52 is then automatically reset by assigning virtualimages 54 first to frames 58, i.e. frames belonging to sheets 32 whichare to be printed on the reverse side, including those sheets 32, whichwere in the position upstream of frame 50, in which the double sheetevent has occurred. Then, the virtual image 54, which was previouslyassigned to the frame 50, in which the double sheet event has occurredis assigned to a frame 50′ following the frames 58, and normal printingoperation resumed. The method described above, thus allows continuousduplex operation of a printing apparatus despite the occurrence of adouble sheet event within the transport path.

The invention has been described above with reference to specificembodiments of the invention, without being limited to these specificembodiments. The scope of the invention is defined by the appendedclaims.

1. A method for controlling the transport of sheets through a printingapparatus having at least one print module and a transport arrangementdefining a direction of transport, arranged for transporting sheets pastsaid at least one print module for printing thereon, said methodcomprising the steps of: (a) setting a print queue by assigning imagesto respective sheets, prior to feeding the respective sheets into thetransport arrangement; (b) feeding sheets into the transportarrangement; (c) detecting whether a double sheet feeding has occurred;(d) deflecting superposed double sheets to a double sheet box, which isarranged upstream of the at least one print module; (e) guiding at leastthose sheets following the superposed double sheet in the transportarrangement, for which an image has already been assigned and which arenot in a duplex path, to a waste box, which is arranged downstream ofthe at least one print module; and (f) automatically resetting the printqueue and continuing to print without stopping the printing apparatus.2. The method of claim 1, wherein resetting the print queue comprisesdeleting the previous assignments of images for those sheets which areguided to the double sheet box and the waste box and reschedulingassignment of these images to respective sheets to be fed into thetransport arrangement.
 3. The method as in claim 1, wherein setting theprint queue is done in a batch manner, wherein a batch of two or moresheets to be printed on a first side is followed by a batch of two ormore sheets, which are in a duplex path and have a print on the firstside and are to be printed on a second side.
 4. The method as in claim1, wherein resetting the print queue comprises deleting the previousassignments of images for those sheets which are in the same batch, inwhich the double sheet event has occurred, and rescheduling assignmentof these images to respective sheets to be fed into the transportarrangement following printing of the sheets in the duplex path.
 5. Themethod as in claim 2, wherein at least one sheet is fed into thetransport arrangement prior to a sheet having a rescheduled imageassignment, which at least one sheet is guided to said waste box, whichis arranged downstream of the at least one print module.
 6. The methodas in claim 1, wherein feeding sheets into the transport arrangement isstopped after detecting a double sheet event until the print queue isreset.
 7. The method as in claim 1, wherein all sheets following thedouble sheet, which have previously been fed into the transportarrangement are guided to said waste box.
 8. The method as in claim 1,wherein a notification is given to an operator, indicating theoccurrence of a double sheet event.
 9. A printing apparatus, comprising:at least one print module; at least one sheet supply including a feeder;a transport arrangement defining a transport path having a direction oftransport, said transport path being arranged for transporting sheetsfrom said sheet supply past said at least one print module to a sheetoutput; a double sheet sensor arranged to sense a double sheet on saidtransport arrangement, said double sheet sensor being arrangeddownstream of said paper supply and upstream of said at least one printmodule in the direction of transport; a double sheet box which isarranged downstream of said double sheet sensor and upstream of said atleast one print module in the direction of transport; a first deflector,operable to selectively deflect sheets on said transport path towardssaid double sheet box; a waste box arranged downstream of said at leastone print module; and a second deflector, operable to selectivelydeflect sheets on said transport path towards said waste box.
 10. Theapparatus as set forth in claim 9, further comprising a proofing trayand a deflector, operable to selectively deflect sheets on saidtransport path towards said proofing tray.
 11. The apparatus as setforth in claim 9, wherein said transport arrangement has a duplexportion, downstream of said outlet, in which a sheet is turned to betransported past the at least one print module for a second time priorto being transported to the outlet.